From Moral Letters to Lucilius/Letter 59:

“The wise man is joyful, happy and calm, unshaken, he lives on a plane with the gods.  Now go, question yourself; if you are never downcast, if your mind is not harassed by my apprehension, through anticipation of what is to come, if day and night your soul keeps on its even and unswerving course, upright and content with itself, then you have attained to the greatest good that mortals can possess.  If, however, you seek pleasures of all kinds in all directions, you must know that you are as far short of wisdom as you are short of joy.  Joy is the goal which you desire to reach, but you are wandering from the path, if you expect to reach your goal while you are in the midst of riches and official titles, – in other words, if you seek joy in the midst of cares, these objects for which you strive so eagerly, as if they would give you happiness and pleasure, are merely causes of grief.”